Lithographie Galvanoformung Abformung Research Articles

Elastic–Plastic Properties of Mesoscale Electrodeposited LIGA Nickel Alloy Films: Analysis of Measurement Uncertainties

Abstract It is well documented that the microstructure and properties of electrodeposited films, such as lithographie, galvanoformung, abformung (LIGA) Ni and its alloys, are highly sensitive to processing conditions hence the literature shows large discrepancies in mechanical properties, even for similar alloys. Given this expected material variability as well as the experimental challenges with small-scale mechanical testing, measurement uncertainties are needed for property values to be applied appropriately, and yet are uncommon in micro- and mesoscale tensile testing studies. In a separate paper, we reported the elastic–plastic properties of 200 μm-thick freestanding films of LIGA-fabricated nanocrystalline Ni-10%Fe and microcrystalline Ni-10%Co, with specimen gauge widths ranging from 75 μm to 700 μm, and tensile tested at strain rates 0.001 s−1 and 1 s−1. The loads were applied by commercial miniature and benchtop load frames, and strain was measured by digital image correlation. In this paper, we examine the measurement uncertainties in the ultimate tensile strength, apparent Young's modulus, 0.2% offset yield strength, and strain hardening parameters, and compare them to the standard deviations. For several of these properties, the standard deviation cannot be interpreted as the statistical scatter because the measurement uncertainty was larger. Microplasticity affects the measurement of the Young's modulus, thus we recommended measuring the modulus after specimens have been cyclically loaded. These measurement uncertainty issues might be relevant to similar works on small-scale tensile testing and might help the reader to interpret the discrepancies in literature values of mechanical properties for LIGA and electrodeposited films.

SensAct: The Soft and Squishy Tactile Sensor with Integrated Flexible Actuator

Herein, a novel tactile sensing device (SensAct) with a soft touch/pressure sensor seamlessly integrated on a flexible actuator is presented. The squishy touch sensor is developed with custom‐made graphite paste on a tiny permanent magnet, encapsulated in Sil‐Poxy, and the actuator (15 μ‐thick coil) is fabricated on polyimide by Lithographie Galvanoformung Abformung (LIGA) micromolding method. The actuator can operate in two modes (expansion and contraction/squeeze) and two states (vibration and nonvibration). The sensor was tested with up to 12 N applied forces and exhibited ≈70% average relative resistance variation (ΔR/Ro), ≈0.346 kPa−1 sensitivity, and ≈49 ms response time with excellent repeatability (≈12.7% coefficient of variation) at 5 N. During simultaneous sensing and actuation, the modulation of coil current, due to ΔR/Ro (≈14% at 2 N force) in the sensor, allows the close loop control (ΔI/Io ≈385%) of expansion/contraction (≈69.8 μm expansion in nonvibration state and ≈111.5 μm peak‐to‐peak in the vibration state). Finally, the soft sensor is embedded in the 3D‐printed fingertip of a robotic hand to demonstrate its use for pressure mapping along with remote vibrotactile stimulation using SensAct device. The self‐controllable actuation of SensAct could provide eSkin the ability to tune stiffness and the vibration states could be utilized for controlled haptic feedback.

Tacsac: A Wearable Haptic Device with Capacitive Touch-Sensing Capability for Tactile Display

This paper presents a dual-function wearable device (Tacsac) with capacitive tactile sensing and integrated tactile feedback capability to enable communication among deafblind people. Tacsac has a skin contactor which enhances localized vibrotactile stimulation of the skin as a means of feedback to the user. It comprises two main modules—the touch-sensing module and the vibrotactile module; both stacked and integrated as a single device. The vibrotactile module is an electromagnetic actuator that employs a flexible coil and a permanent magnet assembled in soft poly (dimethylsiloxane) (PDMS), while the touch-sensing module is a planar capacitive metal-insulator-metal (MIM) structure. The flexible coil was fabricated on a 50 µm polyimide (PI) sheet using Lithographie Galvanoformung Abformung (LIGA) micromoulding technique. The Tacsac device has been tested for independent sensing and actuation as well as dual sensing-actuation mode. The measured vibration profiles of the actuator showed a synchronous response to external stimulus for a wide range of frequencies (10 Hz to 200 Hz) within the perceivable tactile frequency thresholds of the human hand. The resonance vibration frequency of the actuator is in the range of 60–70 Hz with an observed maximum off-plane displacement of 0.377 mm at coil current of 180 mA. The capacitive touch-sensitive layer was able to respond to touch with minimal noise both when actuator vibration is ON and OFF. A mobile application was also developed to demonstrate the application of Tacsac for communication between deafblind person wearing the device and a mobile phone user who is not deafblind. This advances existing tactile displays by providing efficient two-way communication through the use of a single device for both localized haptic feedback and touch-sensing.

Effect of the Properties of Uniformly Patterned Micro-Diamond Pellets on Sapphire Grinding

If nanoscale roughness of machined surfaces is to be achieved, a machining method using a ductile grinding mode is required. If this using a diamond tool is to be realized, uniform patterned micro-diamond pellets must be produced on the tool surface. In this study, uniform patterned micro-diamond pellets were fabricated by using Lithographie Galvanoformung Abformung (LIGA) technology combined with electroplating technology. The effect of the size of the patterned diamond pellet on sapphire wafer grinding was analyzed using a scanning electron microscope and a surface profiler after grinding. As a result, O12 uniformly patterned micro-diamond pellets were fabricated, and a sapphire substrate was ground to obtain a surface roughness (Ra) of 5 nm or less.

Back plate electroplating for high aspect ratio processes

PurposeIn this process the electrical contact is brought to the backside of a standard silicon wafer. The details of the entire process are disclosed, from the photolithography processes to the electrodepositing step, and a model for electrical contact was designed.Design/methodology/approachThe localized Cu growth of high aspect ratio (AR) microstructures was obtained through an SU-8 photolithography by exploiting the optimal adhesion on the silicon surface and the possibility of generating thick layers with a single spun processFindingsThe experimental results showed an unexpected behaviour that is theoretically explained in detail considering the energy band theory. The obtained geometries showed a remarkable 6:1 AR without any adhesion problem. The non-invasive front-side manipulation represents a noteworthy improvement and simplification for the design of a multi-step production process.Originality/valueAn alternative technological approach, called back plate electroplating, has been carried out to obtain Cu growth on the front side of a standard n-type Si wafer through a back side electrical contact. This technique was then applied to fabricate a master for hot-embossing in a LIGA (Lithographie, Galvanoformung, Abformung)-like process flow. For this purpose, an SU-8 thick mask on a standard n-doped wafer was used. Finally, by using this process, it was possible to obtain high AR Cu geometries, avoiding any complex designing and patterning of the contacts on the front side and thus ensuring good adhesion of the SU-8.

Design and property study of micro-slot optics

LIGA (Lithographie Galvanoformung Abformung) as a very useful technique for fabricating devices with micro-scale structures has been reported to make the micro-pore optics (MPO) for years. Light weight is one of the advantages of MPO, making it an alternative for X-ray focusing lenses used on space telescopes. However, researchers seldom considered using the MPO in visible light region. In this article, we designed a micro-slot optics (MSO) similar to MPO and fabricated it by X-ray LIGA technique. The MSO consists of 159 concentric hollow cylinders of nickel with the slot spacings ranging from 59 to 113µm and the focusing property of MSO is studied by simulations and experiments. Both the simulation and experiment results indicate that MSO is a useful focusing element. The MSO has one focal point when the point source is on the principal optical axis with the size of the focal point equaling to the size of the point source.

A novel graphene based nanocomposite for application in 3D flexible micro-supercapacitors

In this work a hybrid graphene-based flexible micro-supercapacitor (MSC) exploiting a novel composite material was fabricated and extensively characterized. The MSC electrodes have been obtained from a synthesized composite aerogel of reduced graphene oxide and polycrystalline nanoparticles of molybdenum (IV) oxide (MoO2) and then dispersed in a solution containing poly(3,4-ethylenedioxythiophene) (PEDOT). Usually in MSCs the electrons have to percolate through the nanostructured Three-dimensional (3D) matrix in order to reach the collectors, made by metal thin films that provide electrical contacts only on the surface of active material. In the attempt to enable a more efficient charge transfer and to allow direct electrical contact without metal deposition, in this study a highly doped PEDOT acting both as current collector and as binder for the nanocomposite material has been employed. 3D MSCs were fabricated through a Lithographie, Galvanoformung, Abformung (LIGA)-like process to obtain high aspect ratio microstructures in polydimethylsiloxane replicas. Capacitance values of 94 F g−1 for the nanocomposite and of 14 mF cm−2 for the device were achieved. Moreover, bending test has demonstrated good performance preservation in a U shape conformation of the device.

Investigation in the interface adhesion strength between SU-8 photoresist and metal substrate by ultrasonic treatment

During the fabrication process of metal microstructures and microdevices by ultraviolet Lithographie Galvanoformung Abformung technology of SU-8, it is common for interface separation and bind failure due to the poor adhesion strength between SU-8 photoresist and metal substrate. In this paper, ultrasonic wave was introduced into the lithography process to improve the interface adhesion strength. Scratch test method was adopted to measure the interface adhesion strengths between SU-8 photoresist and metal substrate without ultrasonic treatment and with ultrasonic treatment under different ultrasonic conditions. The effects and corresponding mechanisms of ultrasonic time and ultrasonic power on the interface adhesion strength between SU-8 photoresist and metal substrate were investigated. The results showed that due to the input of the ultrasonic vibration, the crosslink network characteristics of SU-8 photoresist were changed. The internal stress in SU-8 photoresist was reduced and the interface adhesion strength was improved. The interface adhesion strength firstly increased and then decreased with the increase of ultrasonic time. The maximum interface adhesion work was 0.427 J/m2 at an optimized ultrasonic time of 10 min, which was higher than that of the sample without ultrasonic treatment by 39.5 %. Besides, in the experimental conditions, the interface adhesion strength first increased and then decreased with the increase of the ultrasonic power and the maximum interface adhesion strength attained at the ultrasonic power of 352 W. The ultrasonic treatment method can effectively improve the interface adhesion strength, so as to increase the product yield and performance.

Compound Optical Film Using Gray Scale Mask Embedded with Micro-Voids

This study presents a compound optical film to improve luminance and uniformity to apply in side-LED (Light-emitting diode) backlight module. LIGA (Lithographie GalVanoformung Abformung) technology, soft lithography and homemade gray scale mask were combined to fabricate micro-lens array. Optical film with variable size micro-lens array embedded with micro-voids was designed and manufactured. FRED software was used to simulate optical performance. Micro-voids were quantitatively embedded in the PDMS (Polydimethylsiloxane) optical film. Under the quantitative control of air pressure, those micro-voids inside the optical film can cause light diffusion. The compound optical film with embedded micro-voids, multi aspect ratio and variable size micro-lens array can be fabricated quickly without substrate. Luminance Colorimeter BM-7A from TOPCON was used to carry out the optical measurement. According to the measured data, the compound optical film with embedded micro-voids can enhance the luminance up to 5% and the uniformity up to 6.5% ~ 8.4%. The optical efficiency can be improved via the compound optical film.

Micro-Hot Embossing of Fresnel Lens Using Precision Micro-Featured Mold

Micro-hot embossing process has been widely used in the micromanufacturing. Development of a simple and cost-effective method for fabricating the micro-featured mold insert for micro-hot embossing molding is an important issue. Several techniques such as Si-based micromachining technology, lithographie galvanoformung abformung (LIGA), laser micromachining, micro-electro-discharge machining, micromachining, and deep reactive ion etching have been proposed for fabricating the micro-featured mold insert. However, these methods have some limitations including high cost, complex manufacturing processes, and long processing time. In this study, a simple and cost-effective method for fabricating micro-featured mold with micro-features for microfabrication of polymer was proposed. Effects of micro-hot embossing process parameters on the embossed accuracy of microfeatures were investigated. Results showed that the embossed accuracy of microgroove depth and width increased with both the embossing load and embossing temperature until a saturation value is reached. Based on both cycle time and green manufacturing, an approximately perfect Fresnel lens can be replicated under the embossing load of 50 Kgf and the embossing temperature of 170°C.

Fabrication of electrostatic MEMS microactuator based on X-ray lithography with Pb-based X-ray mask and dry-film-transfer-to-PCB process

Lithographie Galvanoformung Abformung (LIGA) is a promising approach for fabrication of high aspect ratio 3D microactuator for dual-stage slider in hard disk drive. However, this approach involves practically challenging X-ray lithography and structural transfer processes. In this work, electrostatic MEMS actuator is developed based on a LIGA approach with cost-effective X-ray lithography and dry-film-transfer-to-PCB process. X-ray lithography is performed with X-ray mask based on lift-off sputtered Pb film on mylar substrate and photoresist application using casting-polishing method. High quality and high aspect ratio SU8 microstructures with inverted microactuator pattern have been achieved with the interdigit spacing of ~5 μm, vertical sidewall and a high aspect ratio of 29 by X-ray lithography using the low-cost Pb based X-ray mask. A new dry-film-transfer-to-PCB is employed by using low-cost dry film photoresist to transfer electroplated nickel from surface-treated chromium-coated glass substrate to printed circuit board (PCB) substrate. The dry film is subsequently released everywhere except anchor contacts of the electrostatic actuator structure. The fabricated actuator exhibits good actuation performance with high displacement at moderate operating voltage and suitably high resonance frequency. Therefore, the proposed fabrication process is a promising alternative to realize low-cost MEMS microactuator for industrial applications.

Design and fabrication of double-sided optical film for OLED lighting

Design and fabrication of optical films to increase visual brightness of OLED (Organic Light-Emitting Diode) lighting units are presented in this paper. This study explores a new fabrication process combining precision machining, photolithography, and micro forming techniques to make a double-sided optical film. One side of the optical film is made of micro triangular-pyramidal array (MTPA), and the other side is micro gapless hexagonal microlens array (GHMA). First, Taguchi Method is applied to determine the optimal microstructure configuration by the assistance of the commercial optical software, FRED. Second, tungsten (W) mold of MTPA as the first mold is manufactured by precision machining including optical projection grinding, lapping, and polishing processes. Nickel–cobalt (NiCo) mold of GHMA as the first mold of the other side is fabricated by using LIGA (Lithographie Galvanoformung Abformung)-like process. To obtain inverse molds, poly dimethylsiloxane (PDMS) is used to replicate W and Ni–Co molds, which are served as the secondary molds for two sides, respectively. With these molds, UV (ultraviolet) curable resin was used to make double-sided optical film. Then the optical film was packaged on OLED unit to measure its optical properties by PR 650 equipment. The result shows that both brightness and uniformity can be improved by using this film.

Microlenticular lens replication by the combination of gas-assisted imprint technology and LIGA-like process

A mold used in creating diffractive optical elements significantly affects the quality of these devices. In this study, we improved traditional microlens fabrication processes, which have shortcomings, mainly by combining gas-assisted imprint technology and the lithographie galvanoformung abformung (LIGA)-like process. This combination resulted in the production of high-quality optical components with high replication rates, high uniformity, large areas and high flexibility. Given the pixel size of the panel used, the optimal viewing distance, the film thickness and the glass thickness in the formula, we could determine the radius of curvature and the thickness of the lens. By the use of U-groove machining, precise electroforming and embossing to produce polydimethylsiloxane (PDMS) molds, lens film elements can be produced via an ultraviolet (UV)-cured molding process that converts microlenses into flexible polyethylene terephthalate films. In this study, the microlenticular lens mold is fabricated by U-groove machining, Ni electroforming and PDMS casting. Then, the PDMS mold with microlenticular lens structure is used in the gas-assisted UV imprint process and the PET film with microlenticular lens array is obtained. The lenticular lens had a radius of curvature and height of 228 and 18 µm, respectively. A 3D confocal laser microscope was used to measure the radius of curvature and the spacing of the metal molds, nickel (Ni) molds, PDMS molds and the finished thin-film products. The geometry of the final microlenticular lens was very close to the design values. All geometric errors were below 5%, the surface roughness reached the optical level (with all Ra values less than 10 nm) and the replication rate was 95%. The results demonstrate that this process can be used to fabricate gapless, lenticular-shaped, high-precision microlens arrays with a unitary curvature.

Binary blazed grating based on autostereoscopic display mechanism

The diffractive optical element blazed grating is proposed as the beam splitter for autostereoscopic displays in this study. With Lithographie Galvanoformung Abformung and inductively coupled plasma reactive-ion etching, a four-level blazed grating structure is produced. Moreover, highly translucent polydimethylsiloxane is transformed into symmetrical four-level blazed grating films. The experimental results show that the film can successfully transmit the left and the right images to the accurate positions, and the diffraction efficiency is 70.4% and the contrast ratio is above 80%, presenting the original stereoscopic image without it being affected by brightness and crosstalk. In the experiment of stereoscopic imaging, both the left and the right images could be clearly acquired, which proves the feasibility of blazed gratings as practical for the beam splitter of autostereoscopic displays.

Compound Optical Film Using Gray Scale Mask Embedded with Microvoids

This study presents a compound optical film to improve luminance and uniformity to apply in side-LED (light-emitting diode) backlight module. LIGA (lithographie galvanoformung abformung) technology, soft lithography, and homemade gray scale mask were combined to fabricate microlens array. Optical film with variable size microlens array embedded with microvoids was designed and manufactured. FRED software was used to simulate optical performance. Microvoids were quantitatively embedded in the PDMS (polydimethylsiloxane) optical film. Under the quantitative control of air pressure, those microvoids inside the optical film can cause light diffusion. The compound optical film with embedded microvoids, multiaspect ratio, and variable size microlens array can be fabricated quickly without substrate. Luminance colorimeter BM-7A from TOPCON was used to carry out the optical measurement. According to the measured data, the compound optical film with embedded microvoids can enhance the luminance up to 5% and the uniformity up to 6.5% ~ 8.4%. The optical efficiency can be improved via the compound optical film.

Fabrication and design of various dimensions of multi-step ashperical microlens arrays for OLED package

An optical film with aspherical microlens array (A-MLA) by using multi-step lithography process for an OLED (Organic Light-Emitting Diode) package is fabricated, by which method the luminance of OLEDs can be enhanced. The method of design and fabrication of an A-MLA is explored in this study. In the design process, various parameters of an A-MLA such as curved profiles, layout template and dimensions of microlens are analyzed and characterized. Curved profiles include hyperbola, parabola, ellipse and sphere; and layout templates include square, hexagon, triangle and tangential circle. The profile of the A-MLA was determined by using a commercial optical simulation software, FRED. Based on the simulated result, a film with an A-MLA was fabricated using the LIGA-like (Lithographie Galvanoformung Abformung, LIGA) process, including lithography, sputtering, micro-molding with PDMS (Polydimethylsiloxane) and UV (Ultraviolet)-cured technology. The major challenge to this process is to use JSR-126N negative thick photoresist to manufacture an approximate A-MLA optical film with multi-step lithography method. Finally, the films with A-MLAs are attached to an OLED to measure their optical-electric properties. The effectsof A-MLA optical films on OLED luminance are analyzed. In addition, the measured results are compared with simulated ones. They show good agreement with each other.

Design and fabrication compound diffuser film with LIGA-like process

Integrated microlens array (MLA) on an optical film provides interesting application for various fields. In this study, a new type film is developed, called compound diffuser films. Two MLAs on double-side of the film is its feature. Another feature is the shape of the microlens, which is polygonal shape and gapless, i.e. 100% fill-factor. And the compound film can supply functions of diffusing light and enhancing brightness. To obtain the optimal effects of the film, Taguchi method with optical simulation is utilized to design and analyze. Processes of compound films belong to Lithographie Galvanoformung Abformung (LIGA)-like, including lithography, reflow, sputtering, electroplating and replication processes. Among these processes, nickel–cobalt (NiCo) alloy electroplating is a key step to fabricate an accurate and strong template with gapless MLAs, as the first mold. Then, a flexible mold of polydimethylsiloxane (PDMS) is replicated from the first mold, as the secondary mold. Then, the film is manufactured by ultraviolet (UV)-cured method with the secondary mold. The processes have advantages of fast, accuracy and mass production. Finally, this film is measured and analyzed its data. The results of measurement and simulation such as the average intensity and the S/N ratios are compared. They show good agreement with each other.

Copper foil-type vibration-based electromagnetic energy harvester

This paper presents the modeling, simulation, fabrication and experimental results of a vibration-based electromagnetic power generator (EMPG). A novel, low-cost, one-mask technique is used to fabricate the planar coils and the planar spring. This fabrication technique can provide an alternative for processes such as lithographie galvanoformung abformung (LIGA) or SU-8 molding and MEMS electroplating. Commercially available copper foils of 20 µm and 350 µm thicknesses are used for the planar coils and planar spring, respectively. The design with planar coils on either side of the magnets provides enhanced power generation for the same footprint of the device. The harvester's overall volume is 1 cm3. Excitation of the EMPG, at the fundamental frequency of 371 Hz, base acceleration of 13.5 g and base amplitude of 24.4 µm, yields an open circuit voltage of 60.1 mV, as well as 46.3 mV load voltage and 10.7 µW power for a 100 Ω load resistance. At a matching impedance of 7.5 Ω the device produced a maximum power of 23.56 µW and a power density of 23.56 µW cm−3. The simulations based on the analytical model of the device show good agreement with the experimental results.

Fabrication of various dimensions of high fill-factor micro-lens arrays for OLED package

Organic light-emitting diode (OLED) has been the subject of much interest in the lighting and display module. This study focuses on how to enhance brightness and scatter through a micro-lens array (MLA) with high fill-factor. A LIGA-like (Lithographie Galvanoformung Abformung, LIGA) process was applied to the fabrication process because it has good replication for microstructures. Seven kinds of micro-lens arrays with different dimensions were designed. These dimensions with different aspect ratio were divided into two groups, i.e. gapless high fill-factor and low fill-factor with gap. They were used to compare their optical properties of brightness with each other. In addition, a controllable method was also developed to design the contour of a micro-lens. Then, a metallic mold with MLA was fabricated by nickel–cobalt (NiCo) electroplating process. A highly accurate and strong mold can be obtained. Finally, a UV (ultraviolet) curable polymer was used as the material of an optical film in this replication process of a MLA. After these optical films with MLAs were obtained, an optical microscope (OM) and a photometer were used to measure and characterize the optical results. The experimental results of the MLA were compared with those of the design.

Low cost, high performance, self-aligning miniature optical systems

The most expensive aspects in producing high quality miniature optical systems are the component costs and long assembly process. A new approach for fabricating these systems that reduces both aspects through the implementation of self-aligning LIGA (German acronym for lithographie, galvanoformung, abformung, or x-ray lithography, electroplating, and molding) optomechanics with high volume plastic injection molded and off-the-shelf glass optics is presented. This zero alignment strategy has been incorporated into a miniature high numerical aperture (NA = 1.0 W) microscope objective for a fiber confocal reflectance microscope. Tight alignment tolerances of less than 10 microm are maintained for all components that reside inside of a small 9 gauge diameter hypodermic tubing. A prototype system has been tested using the slanted edge modulation transfer function technique and demonstrated to have a Strehl ratio of 0.71. This universal technology is now being developed for smaller, needle-sized imaging systems and other portable point-of-care diagnostic instruments.